The present invention relates to a virtual path tracing method and apparatus wherein the operational information of virtual paths are collected through OAM (operation and maintenance) cells for the purpose of managing an ATM (asynchronous transfer mode) network architecture.
A known path tracing method intended to manage a network architecture is a method based on an SDH (synchronous digital hierarchy) which is defined in "CCITT (Comite Consultatif International Telegraphique et Telephonique) Recommendation G. 709". A detailed paper concerning the path tracing of SDH is `Yasuda et al.: "Proposal of Method of Tracing Connection System and Automatically Collecting Network Equipment Data by Utilizing SDH Frame Structure", Technical Bulletin of the Institute of Electronics, Information and Communication Engineers of Japan, IN90-50, pp. 31-36`.
The path tracing method in the SDH will be explained with reference to FIGS. 8 and 9 of the accompanying drawings.
FIG. 8 illustrates the format and arrayal of path trace information in the SDH. In the SDH path tracing, the path trace information are affixed to overhead areas of predetermined time slots and are iteratively transmitted by a path terminator located on a transmitting side. Shown in FIG. 8 is only the arrayal of the path trace information (of J1 [bytes]) in the path terminator. The path trace information denoted by numeral 100 is formed of a series of character data of 64 [bytes], and it bears logical name information 102 in the path terminator. Besides, a delimiter 101 for indicating the break of the character data series is affixed at the tail of this series. Since the end of the path trace information is indicated by the delimiter 101, the path trace information 100 can also be set as character data exceeding 64 [bytes]. In addition, symbols (#k-1), (#k), (#k+1), (#k+2), . . . annexed to the path trace information signify that the same information is iteratively output. The logical name information 102 is indicated in VC-3 (virtual container 3) unit and VC-4 unit. The expressions "VC-3" and "VC-4" indicate the hierarchical levels of digital transmission. By way of example, the level VC-3 corresponds to a transmission rate of 50 [MBPS], and the level VC-4 a transmission rate of 150 [MBPS].
FIG. 9 illustrates the form in which the path tracing in the SDH is realized. Shown in the figure is a construction in which the path trace information is transmitted from the path terminator 110 located on the transmitting side and is received by a path terminator 114 via a VC-3/VC-4 path network 113. In the path terminator 110 on the transmitting side, a path trace information generating circuit 112 is previously furnished with information on a logical name and attributes. The circuit 112 generates the path trace information shown in FIG. 8 on the basis of the given information, and it inserts the generated information into the path overhead of J1 [bytes] via a transmitting-side path terminating circuit 111. A receiving-side path terminating circuit 115 included in the path terminator 114 on a receiving side, separates the path trace information of J1 [bytes], detects the delimiter 101 indicating the break of the character data series and regenerates the character data series of 64 [bytes]. Further, a path trace information checking circuit 116 collates the received and regenerated character data series with the logical name and attributes of the transmitting side given as expected values beforehand. In a case where the paths at the VC-3 and VC-4 levels are correctly connected, the received path trace information agrees with the expected values. On the other hand, in a case where the paths are erroneously connected, the received path trace information disagrees with the expected values.
In the SDH in which the information is transmitted in an STM (synchronous transfer mode), the normalcy of the path connection between a transmitting-side path termination point and a receiving-side path termination point is acknowledged by the method stated above.
Next, a method of tracing paths in an ATM (asynchronous transfer mode) will be stated as the second prior-art technique. The ATM has a management unit called a "virtual path (VP)", in correspondence with the virtual container of the SDH. With the ATM, in managing a network in VP unit, operation and maintenance information is transferred using an OAM (operation and maintenance) cell as fundamentally stipulated by CCITT Recommendation I. 610. According to the fundamental principle, it is considered that the trace information of the virtual path will also be transferred on a cell basis by the use of the OAM cell. By the way, in the ensuing explanation, the function of tracing the virtual path shall be shortly called the "VP tracing", while the OAM cell which is used for tracing the virtual path shall be called the "VP tracing cell".
FIG. 10 illustrates the form in which the VP tracing function is realized, and which is naturally derived from the above premises. The form shown in FIG. 10 is the same as stated in `Matsunaga et al.: "Proposal of Virtual Path Tracing System in ATM Network", Lecturing thesis B-482, the Autumn National Meeting of the Institute of Electronics, Information and Communication Engineers of Japan, 1991`. In FIG. 10, four VP connectors 120.about.123 are arranged between the first VP terminator 124 and the second VP terminator 125. These VP terminators 124 and 125 are devices which terminate the virtual paths, and each of which is an ATM exchange, an ATM terminal, or the like. 0n the other hand, the VP connectors 120.about.123 are devices which set the route of the cells in virtual path unit, and each of which is an ATM cross connection device or the like. Identification Nos. (XC-ID) are affixed to the VP terminators 124 and 125 in advance. An operating system (hereinbelow, expressed as "OpS") 126 is connected to the VP connector 120 serving as the start point of the paths and to the VP connector 123 serving as the end point of the paths. The OpS 126 is a control center for operating and maintaining the ATM network. By way of example, the OpS 126 can perform the continuity test of the VP's, acknowledge the route of the VP's and update the database of the network architecture management.
Now, the operation of tracing the virtual paths in the construction shown in FIG. 10 will be explained.
First, a command for performing the VP tracing is sent from the OpS 126 to the VP connector 120. Upon receiving the command, the VP connector 120 generates a VP tracing cell 130. It writes the operational information a of its own into the generated cell, and thereafter sends out the resulting cell as a VP tracing cell 130 to the ATM network. The VP connector 121 discriminates the cell 130 received from the VP connector 120, as the VP tracing cell, and it separates and holds this VP tracing cell 130. Further, it affixes the operational information b of its own to the VP tracing cell 130 and thereafter sends out the resulting cell as a VP tracing cell 131 to the succeeding stage. The VP connector 122 operates similarly to the VP connector 121. The VP connector 123 discriminates a cell 132 received from the VP connector 122, as the VP tracing cell, and it separates and holds this VP tracing cell 132. Further, it affixes the operational information d of its own to originate network operating information 133 and sends the resulting cell back to the OpS 126.
In this way, the operational information at the respective nodes of the ATM network can be read into the operating system 126 which integratively controls the network.
The individual VP connectors for executing the VP tracing shall be classified into three types and have their appellations defined as follows:
1 Tracing start point;
Intended to mean the VP connector which generates the VP tracing cell and then sends it out to the ATM network at the command of the OpS 126. In FIG. 10, the VP connector 120 corresponds to this type.
2 Tracing relaying point;
Intended to mean the VP connector which separates the VP tracing cell from the ATM network, and which writes the operational information of its own into the separated cell and thereafter sends out the resulting cell to the ATM network again. In FIG. 10, the VP connectors 121 and 122 correspond to this type.
3 Tracing end point;
Intended to mean the VP connector which separates the VP tracing cell from the ATM network, and which informs the OpS 126 of the operational information borne in the separated cell. In FIG. 10, the VP connector 123 corresponds to this type.
Of the two prior-art techniques stated above, the first one which is the path tracing method utilizing the path overhead has the drawback that a section for executing the path tracing is so limited as to extend between the termination points of the VC-3 or the VC-4. Therefore, this method is not applicable to the tracing of the virtual paths (the VP tracing) in the ATM network.
On the other hand, the second prior-art technique which is the method employing the VP tracing cells is problematic as stated below. As compared with the conventional STM network, the ATM network is subject to the dynamic change of the network architecture. When this condition is considered, the VP tracing requires, not only the function of acknowledging the continuity between the VP termination points, but also the function of collecting the information on the route of the VP's. In the explanation of the second prior-art technique, this function corresponds to the operations of writing the operational information of the VP connectors into the VP tracing cells and finally informing the operating system of the written operational information. To be noticed here is the fact that the total value of the operational information of the VP connectors, which belong to the route of the VP's to be traced, can exceed the capacity of the payload of each cell. The "payload" of the cell signifies the area of the cell except the header part thereof. Since the length of the cell is fixed to 53 [bytes], the payload area is limited to the capacity of 48 [bytes]. In spite of the limited capacity, the operational information are affixed at the respective VP connectors, so that the total value thereof can become greater than the capacity of the payload of the cell. In carrying out the VP tracing, therefore, the operational information of the VP connectors need to be divided and be distributively borne by a plurality of VP tracing cells. In the aforementioned thesis "Proposal of Virtual Path Tracing System in ATM Network", the necessity of pluralizing the VP tracing cell is referred to, but a concrete processing algorithm is not presented.
The principal problems to be solved in realizing the processing algorithm are as follows:
(1) Method of specifying a VP tracing cell to have operational information written thereinto, among pluralized VP tracing cells. PA1 (2) Decisional condition for pluralizing a VP tracing cell, and method of pluralizing the VP tracing cell. PA1 (3) Method of deciding the end of VP tracing. PA1 (4) Methods of coping with the error and loss of a VP tracing cell.